The valve has been used to advantage in a circulating hot oil system to maintain nearly constant oil flow through a pump and/or heat exchanger regardless of the oil demand by the remainder of the system. FIG. 4 is a schematic diagram of such a hot oil system. Oil is routed to the various loads in response to a temperature or other controller. When all load valves are fully open, oil flow through the pump and heat exchanger would be much greater than with all load valves closed, if the weight controlled valve were not present in the system.
This valve provides a means of by-passing oil back to the pump suction, thereby maintaining flow through the heat exchanger. The weight controlled valve maintains a nearly constant pressure difference between the supply and return manifolds so that any load receives the same quantity of oil regardless of the number of other loads in service.
The weight controlled valve differs from existing technology as follows. Currently, either spring loaded relief valves or actively controlled throttling valves are used to bypass oil when not required by the loads. The pressure drop through spring loaded valves increases as flow through the valve increases. The difference in manifold pressure from supply to return is a function of the number of loads in service. Further, the springs used in spring type relief valves are subject to deterioration with temperature and number of operating cycles.
An additional disadvantage to spring type relief valves is that the necessary variation of pressure through the valve with flow can reduce flow through the heat exchanger as loads are turned off, especially if a centrifugal pump is used. This can cause overheating of the oil due to low velocities on the heat exchanger and may increase pump power and wear as well. Actively controlled throttling valves can avoid most of these problems but are prohibitively expensive for many applications.